Rapid Visco Analyser Viscosity Research Articles

Functional properties of milk protein concentrate and micellar casein concentrate as affected by transglutaminase treatment

Milk protein concentrate (MPC) and micellar casein concentrate (MCC) are used in foods to increase protein content and improve functional properties. The use of cross-linking enzymes such as transglutaminase (TGase) has the potential to modify the physical properties of MPC or MCC and may improve their functional properties. The objective of this study was to determine the effect of TGase treatment of MPC and MCC retentates on the functionality of MPC and MCC. MCC and MPC retentates were produced and treated with TGase enzyme at three levels, namely 0.0 TGase addition (control), 0.3 units/g of protein, and 3.0 units/g of protein. Treated retentates were then spray dried and various functional properties, including water (WAC) and fat (FAC) absorption capacity, alcohol (AS) and heat (HS) stability, solubility, solubility index (SI), effect of calcium chelating salts, and glucono-δ-Lactone (in yogurt like formulation) were tested. MPC samples had significantly (P ≤ 0.05) higher AS, HS, solubility, higher yogurt viscosity, water holding capacity (WHC), and syneresis, and significantly (P ≤ 0.05) lower SI, WAC, and FAC as compared with respective MCC treatments. TGase treatment significantly increased the AS, HS, SI, and significantly (P ≤ 0.05) decreased solubility. In MCC yogurt samples, there was a significant (P ≤ 0.05) decrease in rapid visco analyzer viscosity, WHC, and syneresis as enzyme levels increased. The effect of calcium chelating salts was more pronounced at a higher TGase level. The study demonstrates that TGase treatment will significantly affect and modify the functionality of MCC and MPC.

Functional and physicochemical properties of Durian seed flour blended with cassava starch

Durian (Durio zibethinus Murr.) seed flour (DSF) has very soft gel with high syneresis. Blending it with cassava starch (CS) could deliver strongly advantageous effects. The objective of this work was to investigate the functional and physicochemical properties of blends of CS and DSF. Experimentally, commercial cassava starch CS (18.18 ± 0.11% amylose) was blended with DSF (containing 55.44 ± 4.93% gum and 14.62 ± 0.07% amylose) in various CS/DSF ratios: 100/0, 90/10, 80/20, 70/30, 60/40, 50/50, 40/60, 30/70, 20/80, 10/90, and 0/100 by dry weight. The key properties of those blends were investigated, namely swelling power (SP), solubility, pasting properties by the Rapid Visco Analyzer (RVA), gelatinization temperature, and gel texture and syneresis. CS showed lower SP at 60 °C, but higher SP at 75 and 90 °C than DSF, while DSF had higher solubility than CS at all temperatures tested. The blends had SP and solubility between these extremes. RVA viscosities for all ratios of the CS/DSF blends were often below those of the individual components, with DSF influencing more than expected from its proportion. The peak viscosity (PV) of CS was significantly higher than that of DSF (3955 ± 37 vs. 1918 ± 17 mPa.s). The PV of CS/DSF blends with 10/90–60/40 ratios was slightly different from that of DSF, but increased strongly for the 70/30- 90/10 ratios. As regards gelatinization, CS had lower temperature range (62.66 ± 0.13–72.06 ± 0.21 °C,) than DSF (67.50 ± 0.55–79.35 ± 0.16 °C), while its enthalpy was higher (12.83 ± 0.81 vs. 5.38 ± 0.16 J/g). All the blends showed higher gelatinization temperature than CS but lower than DSF and their enthalpies had the opposite trend. Regarding the gel properties, gel hardness of CS was about five-fold higher than that of DSF (50.9 ± 30.27 vs. 9.59 ± 0.67, p < 0.05), while syneresis of CS was much lower (1.61 ± 0.33 vs. 58.30 ± 0.44%, p < 0.05) than of DSF. For their blends, it turned out that gel hardness increased and syneresis decreased with CS content in the blend. The gel hardness was synergistic for 90/10 and 80/20 ratios with about 50% increase over the pure components, and simultaneously the syneresis relative to plain DSF was reduced by over 50%. The results suggested that improved DSF properties can be achieved by blending with CS, and also a small amount of DSF (10–20%) has synergistic effect on gel hardness of the blend. Gum in the DSF plays an important role in the continuous phase of the paste and the gel.

Effect of blending and pregelatinizing order on properties of pregelatinized starch from rice and cassava

The aim of this work was to investigate the effects of processing order by mixing and pregelatinizing on properties of pregelatinized starch blends of cassava (C) and rice (R) starches, either mixed in various ratios (0, 10, 30, 50, 70, 90 and 100%C) before pregelatinizing (MP) or with that order exchanged (PM, for pregelatinizing the components before mixing). Starch solids of 45% in water were pregelatinized using double drum drying at 120oC. The water absorption index (WAI) and water solubility index (WSI) were measured, and pasting properties were characterized using Rapid Visco Analyzer (RVA). The results showed that MP (30 - 70%C blends) had WSI half of that of PM, while with 10%C the former gave the higher WSI. In RVA viscosities, especially the hot peak viscosity, MP cases had significantly higher values (p&lt;0.05) than PM for all mixing ratios, indicating interactions in MP and less degradation of starch molecules. The choice of processing order gives some additional control over pregelatinized starch blend behavior in water, while a larger range of control is available by selection of the blend proportions.

Effect of carboxymethyl cellulose on properties of wheat flour-tapioca starch-based batter and fried, battered chicken product

Hydrocolloid is widely used to improve the quality of food. In this study, the effect of carboxymethyl cellulose (CMC) on the properties of batter and fried, battered product prepared from wheat flour (WF)-tapioca starch (TS) blends was investigated. The dry-mixes were prepared from the flour blends of 91.4% flour blend [WF/TS (1:1) and CMC (0%, 0.25%, 0.5%, 0.75% or 1.0%)], 5.5% salt and 3.1% leavening agent and then mixed with water (1:1.3) for batter preparation. The batters had a significant increase in consistency coefficient, yield stress and batter pickup with increasing CMC replacement in the dry mix. However, CMC did not significantly (p > 0.05) alter either the differential scanning calorimetry thermal properties of the batters or the rapid visco-analyzer viscosity after holding at 95 °C for 4 min. The substitution of CMC decreased the oil content but increased the moisture content in the pre-fried chicken wing sticks. After final frying at 180 °C, the oil content of the fried product was significantly (p < 0.05) reduced in the samples containing CMC (equal to or more than 0.5% in dry-mix). There were no significant (p > 0.05) differences in the overall liking scores in the fried products without and with 0.5% CMC replacement in the flour blend. The results indicated that CMC could be used in WF/TS batter preparation, enhancing the batter pickup and quality and especially acting as an oil barrier-forming ingredient for fried, battered foods.

Modelling and Comparison of Wheat Flour Extrusion Cooking Behaviours in Two Different Twin-Screw Extrusion Systems

The aim of this study was to investigate the extrusion cooking behaviours of two wheat flour samples (W1DK, W2CH) in two different twin-screw extrusion systems, where the wheat flour samples were characterised by rapid visco analyser (RVA) measurements. A new method is proposed to model and compare the wheat flour extrusion behaviours in the two systems through the RVA measurements, an extrudate bulk density model and a melt viscosity calculation. A new method is suggested to calculate the melt viscosity in the extrusion process. The average viscosity value of the W1DK sample was 64% higher than that of the W2CH sample in the RVA measurements. The comparison results show that the high viscosity for W1DK obtained from the RVA corresponds to a high reduced melt viscosity (η r , (1/s)γ) for W1DK, i.e., η r = 0.25–2.61 (1/s)γ (η r = 0.042–0.082 (1/s)γ for W2CH), a high specific mechanical energy (SME) for W1DK, i.e., SME = 8.16–11.28 kJ/kg (SME = 5.57–9.99 kJ/kg for W2CH) and a low extrudate bulk density (ρ B ) for W1DK, i.e., ρ B = 185–488 g/L (1 g/L = 1 kg/m3) (ρ B = 406–510 g/L for W2CH) in the two extrusion systems. The RVA viscosity and the calculated melt viscosity can be used to identify a recipe characteristic in terms of torque and extrudate bulk density in the two extrusion systems. A comparison has also been made for the bulk density model and response surface methodology in the extrudate bulk density prediction.

Effect of the phytate and hydrogen peroxide chemical modifications on the physicochemical and functional properties of wheat starch

To investigate the characteristics of chemically modified wheat starch, such as oxidized (OWS), cross-linked (CLWS) and dual-modified wheat starches, cross-linked oxidized (COWS) and oxidized cross-linked (OCWS) wheat starches were obtained by 12% hydrogen peroxide (H2O2) and 2% sodium phytate treatments, respectively. After modifications of wheat starch by cross-linking and oxidization, it was determined that native wheat starch was effectively modified with respect to the structure and physicochemical characteristics, as detected by Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), Rapid Visco Analyzer (RVA), scanning electron microscopy (SEM) and X-ray diffraction (XRD). DSC analysis demonstrated that peak temperature (Tp) 64.41°C of the COWS was the highest. The RVA viscosity indexes of CLWS were noticeably increased compared with the other four starches, of which three oxidized starch samples showed lower RVA profiles because of oxidation. The XRD result indicated that cross-linked phosphates from sodium phytate were primarily located in the amorphous regions of starch granules. After modifications by different treatments, the starch samples exhibited different morphological characteristics, including A-type and B-type wheat starch granules, which showed much closer contact with each other by the cross-linking reaction under SEM observations. The functional characteristics, including solubility, swelling power, light transmittance and freeze-thaw stability (FTS), of all five treated and untreated wheat starches demonstrated that COWS had the highest solubility at 0.57 and that CLWS showed the best swelling power at 12.63 (g/g). The paste clarity of COWS was improved to 47.72% higher than that of native starch (7.54%), and the water loss of COWS (21.62%) was the lowest, which is beneficial to the production of quick-frozen food. Our results showed that dual-modified starch by using sodium phytate and hydrogen peroxide had significantly altered structural and functional properties. The present study provides fundamental information of dual-modified wheat starch for its potential industrial application.

Detection of Incipient Germination in Malting Barley with a Starch Viscosity Method and a Proposed Ethanol Emission Method

The risk of germination loss during storage in two‐row malting barley can be reduced by identifying grain lots that have undergone incipient germination (IG) during harvest. A method based on starch viscosity that utilizes a Rapid Visco Analyzer (RVA) is currently available for IG analysis. A new potential method, based on the measurement of ethanol emission (EE) from whole barley, may be more efficient and less expensive than the RVA procedure. Three storage experiments were performed: experiments 1 and 3 at 25°C and 80% rh, and experiment 2 in unheated, uninsulated buildings. Decline in germination energy (GE) varied from &lt;1% to about 80% during storage. In experiments 1 and 3, R2 for GE loss (expressed as [weeks to 5% loss of GE]0.2) versus EE was 0.76 in both cases, whereas R2 for GE loss versus RVA viscosity was 0.64 and 0.68, respectively. In experiment 2, the greatest loss of GE was associated with high temperatures and relative humidity in July and August. EE performed as well as RVA in the prediction of germination loss in all three trials. Although further evaluation of the EE method is required, it appears to be a promising alternative to the RVA technique.

Profile Optimisation for the Determination of Pasting Properties of Bamboo Seed Flour

The present investigation was to optimise the pasting profile specific to the determination of pasting properties of bamboo seed flour using Rapid Visco Analyser (RVA). The RVA test procedure profile conditions such as shear rate (A), flour concentration (B) and initial/final temperature (C) for bamboo seed flour in standard 1 profile (TCW software) was optimized using Central Composite Rotatable Design of Response Surface Methodology. The center point in five level factor for independent variables of A, B and C was 160 rpm, 4g and 50°C respectively. The shear rate, starting and ending temperature had negative significant influence (p<0.01) on RVA viscosity parameters while flour concentration showed positive significant effect (p<0.01) on RVA viscosity parameters. Interactively, flour concentration and temperature suggested significant negative influence (at p<0.05) on all determined RVA viscosity parameters. On the basis of maximum peak (PV) and Final Viscosity (FV), 123 rpm as rotational speed of paddle, 3.9g as flour concentration mixed in 25 ml of water (15.6%) and 32.3°C as starting and ending temperature in standard 1 profile of RVA test procedure was considered as valid profile conditions for the determination of pasting properties of bamboo seed flour.

Application of the Rapid Visco Analyzer (RVA) as an Effective Rheological Tool for Measurement of β‐Glucan Viscosity

ABSTRACTThe physiochemical characteristics of β‐glucan in oat and barley foods can affect human physiological response. A method for continuous measurement of β‐glucan viscosity with a Rapid Visco Analyzer (RVA) was developed to overcome the complexity of the common protocols based on in vitro digestion methods. The effects of several parameters on viscosity and solubility were considered. Oat cereal foods showed different RVA viscosity profiles depending on their physiochemical characteristics. Products high in starch exhibited a high initial viscosity that was reduced by α‐amylase action, whereas products with low amounts of starch exhibited a slow increase in viscosity. The viscosity of all samples reached a plateau in the viscosity curve after 1–2 hr, which is the key for obtaining reproducible results. Optimum digestion condition was achieved using sodium phosphate buffer (pH 6.9) and 1% β‐glucan dispersion at 37°C and 160 rpm. A particle size of &lt;0.6 mm gave more consistent viscosities than did larger particles without affecting the solubility of β‐glucan. Pancreatin and α‐amylase concentrations affected the viscosity profile by influencing the digestion rate of protein and starch in the samples, but pepsin had limited influence at pH 6.9. Highly significant Pearson correlation between the in vitro digestibility protocol and RVA methods was achieved, indicting that the developed method could be used as an effective alternative for measurement of β‐glucan viscosity.

Characterisation of grain quality in diverse sorghum germplasm using a Rapid Visco-Analyzer and near infrared reflectance spectroscopy

Twenty-two diverse sorghum landraces, classified as normal and opaque types obtained from Ethiopia, were characterised for grain quality parameters using near infra-red spectroscopy (NIRS), chemical and Rapid Visco-Analyzer (RVA) characteristics. Protein content ranged from 77 to 182 g kg(-1), and starch content from 514 to 745 g kg(-1). The NIRS analysis indicated the pig faecal digestible energy range from 14.6 to 15.7 MJ kg(-1) as fed, and the ileal digestible energy range from 11.3 to 13.9 MJ kg(-1) as fed. The normal sorghums had higher digestible energy than the opaque sorghums, which exhibited lower RVA viscosities, and higher pasting temperatures and setback ratios. The RVA parameters were positively correlated with the starch content and negatively correlated with the protein content. The normal and opaque types formed two distinct groups based on principal component and cluster analyses. The landraces were different for the various grain quality parameters with some landraces displaying unique RVA and NIRS profiles. This study will guide utilisation of the sorghum landraces in plant improvement programs, and provides a basis for further studies into how starch and other constituents behave in and affect the properties of these landraces.

Mechanism of gliadin–glutenin cross-linking during hydrothermal treatment

The gluten proteins, gliadin and glutenin, are important for wheat flour functionality and they undergo changes during heat treatment involving sulfhydryl (SH) groups. To change the level of SH-groups during hydrothermal treatment, the oxidant, potassium iodate (2.1 μmol/g protein) and the reducing agent dithiothreitol (DTT, 6.1 μmol/g protein) were added to 20% (w/w) gluten-in-water suspensions at room temperature, at 90 °C and after 15 min at 95 °C, and the viscosity was measured by the Rapid Visco Analyser (RVA). Protein extractabilities after hydrothermal treatment were determined by size-exclusion and reversed-phase HPLC. DTT decreased maximal RVA viscosity and the levels of extractable α- and γ-gliadin and this decrease was independent of the time of addition during hydrothermal treatment. In contrast, potassium iodate increased the levels of extractable α- and γ-gliadin. Its impact was less when added at later times during RVA analysis. A SH-blocking agent ( N-ethylmaleimide, 8.0 μmol/g protein), added at room temperature to the gluten suspension, decreased RVA viscosity at 95 °C and increased the extractabilities of glutenin and α- and γ-gliadin after hydrothermal treatment. Subsequent addition, at 90 °C, of a reducing agent (glutathione, 3.1 and 6.2 μmol/g protein) recovered the control RVA profile and restored the control protein extractabilities after RVA analysis. This shows the importance of heat-induced gliadin–glutenin reactions for gluten viscosity and of the presence of free SH-groups for the polymerization of gluten proteins. A model explaining gliadin–glutenin polymerization through a sulfhydryl-disulfide exchange mechanism and demonstrating the effects of redox agents is put forward.

Effect of wheat puroindoline alleles on functional properties of starch

Puroindoline a and b (Pina, Pinb) form the molecular basis of bread wheat grain hardness. Varieties with a softer endosperm and a wild genotype, in which both Pina and Pinb were present, seemed to produce less damaged starch flour than hard varieties, where Pin mutations occurred and changed the starch rheological properties. The functional property of starch samples extracted from wheat varieties with different Pin alleles was evaluated. Starch morphology was characterized by scanning electron microscopy and laser light scattering. Thermal properties were evaluated by differential scanning calorimetry. Amylose content, starch damage and rapid visco-analyser (RVA) parameters were also determined. Significant variations (P < 0.05) were identified between different Pin variants for the distribution pattern of starch granule volume, amylose content, starch damage, RVA viscosity breakdown and retrogradation, gelatinisation transition temperatures and enthalpies. Hard genotypes presented higher medium diameter granules and lower enthalpic values. However, the differences detected are more evident among varieties that present both Pina and Pinb, than among those presenting only one of the two (a or b).

Impact of redox agents on the physico-chemistry of wheat gluten proteins during hydrothermal treatment

The impact of the oxidants potassium bromate and potassium iodate and the reducing agent dithiothreitol (DTT) on the rheological behaviour of 20% (w/v) gluten-in-water suspensions during thermal treatment was monitored with the rapid visco analyser (RVA). The suspensions were subjected to a linear temperature increase from 40 to 95 °C in 14 min, a holding step of 40 min at 95 °C, a cooling step (7 min) with a linear temperature decrease to 50 °C, and a final holding step at 50 °C (13 min). Potassium iodate (1.18 and 1.77 μmol/g protein) and potassium bromate (1.52 and 15.2 μmol/g protein) decreased RVA viscosities in the holding step and increased sodium dodecyl sulphate (SDS) protein extractabilities suggesting a greater heat resistance and decreased gliadin–glutenin cross-linking. In contrast, in the presence of DTT (1.65 and 3.30 μmol/g protein) RVA viscosity increased at lower temperatures and lowered SDS extractabilities. It is postulated that low concentrations of reducing agent facilitate gliadin–glutenin cross-linking during heating while oxidants hinder gluten polymerization due to decreased levels of free sulphydryl groups and less flexibility of the glutenin chains.

Impact of Proteins on Pasting and Cooking Properties of Nonparboiled and Parboiled Rice

ABSTRACTThe role of proteins in the pasting and cooking properties of non‐parboiled (npb) and parboiled (pb) rice was tested by means of a reducing agent dithiothreitol (DTT) and a protease (trypsin). DTT increased the swelling power and carbohydrate leaching of flour from npb rice flour but decreased its amylose leaching. Although DTT slightly increased the Rapid Visco Analyser (RVA) viscosity at the initial stages of the pasting process, it decreased RVA viscosity in the further phases of the experiment. Preincubation of flour with a trypsin decreased RVA viscosity along the whole temperature profile. Addition of DTT to the cooking water decreased water absorption and rice hardness and increased leaching of solids during cooking and stickiness of the cooked npb rice. Addition of DTT to the cooking water of flour from pb rice increased swelling power, carbohydrate leaching, and amylose leaching. Addition of DTT also increased RVA viscosity. Preincubation with trypsin had a similar effect but the changes were less pronounced. Addition of DTT increased stickiness of cooked pb rice and increased water absorption and leaching of solids during cooking. Taken together, the results provide evidence for the existence of a protein barrier affecting starch swelling, rheological, and cooking properties of both npb and pb rice.

Functionality Behavior of Raw and Extruded Corn Starch Mixtures

ABSTRACTRelationships between the structural properties of raw and extruded corn starches and their functionalities were investigated using mixtures of these starch types. Extruded starch had higher water absorption and water solubility indices, and produced lower RVA viscosity profiles when compared with raw starch. It also had no differential scanning calorimetry (DSC) endotherm. Gel cohesiveness and adhesiveness of both starch types were similar, while extruded starch gels were softer. Extruded starch produced lower Rapid Visco Analyser (RVA) viscosity profiles than raw starch due to starch degradation during extrusion. The raw and extruded starch components had negative interaction coefficients, thus RVA viscosity parameters were lowered as the fraction of extruded starch in the mixture increased. Starch degradation in the extruded starch was a likely significant factor associated with low viscosity profiles. Mixtures of raw and extruded starches could be commercially prepared to obtain finished starch products with a range of functional attributes.

The Rapid Visco Analyzer (RVA) as a tool for differentiating potato cultivars on the basis of flour pasting properties

Potatoes of two cultivars representing extremes in potato texture, Russet Burbank (mealy) and IdaRose (waxy), were lyophilized, ground into flour, and analyzed with a Rapid Visco Analyzer (RVA) to identify flour pasting characteristics unique to each cultivar. A factorial experiment, which included multiple levels of heating rate, peak temperature, and flour concentration, was employed to assess RVA run parameter association with flour pasting behaviors and the potential to differentiate cultivars according to the responses. Pasting profiles of the potato flour provided a unique functional finger-print for each cultivar flour, which embodies structural and molecular components of the native potato tissue. Pasting profile viscosity attributes were influenced by variable levels of heating rate, peak temperature, and flour concentration. At increasing flour concentrations, RVA viscosity attributes increased in magnitude, but possessed similar pasting curves. A variable heating rate primarily affected events occurring early within the pasting profile (time to gelatinization, time to peak viscosity, peak viscosity), while changes in peak temperature influenced viscosity attributes (trough viscosity, breakdown, final viscosity, total setback) associated with the latter portion of the viscosity curve. A high peak temperature generally resulted in increased breakdown and total setback and decreased trough and final viscosities. RVA viscosity attributes, time to gelatinization, peak viscosity, breakdown, and final viscosity were identified as potential characteristics for cultivar differentiation. Discrimination of the cultivar extremes was affected by RVA run parameters, and was maximized at moderate heating rates (4 to 6 C min-1), moderate to high levels of peak temperature (85 to 90 C), and intermediate flour concentrations.

Rheological and physicochemical properties of starches from moist- and dry-type sweetpotatoes.

Although starch makes up from 50 to 70% of sweetpotato (SP) dry matter, its role in cooked texture is unknown. The purpose of this research was to characterize raw starches isolated from SP cultivars and experimental selections (C/S) with a wide range of textural properties when cooked and to investigate the relationship between textural properties of the cooked roots and characteristics of the isolated starches. Shear stress measured by uniaxial compression of cooked SP cylinders served as an objective measure of SP texture. Starches were isolated from C/S representing three SP texture types: moist (Jewel and Beauregard); intermediate (NC10-28 and NC2-26); and dry (NC6-30 and NC8-22). The following parameters of isolated starches were measured: amylose content by colorimetric and differential scanning calorimetric (DSC) methods; swelling power, solubility, gelatinization enthalpy (DeltaH), and pasting properties by Brabender amylograph (BA) and rapid viscoanalyzer (RVA). Pasting temperatures for SP C/S measured by BA and RVA were significantly correlated. Due to high shear degradation in RVA, RVA viscosities of starch suspensions decreased as much as 40% during cooking at 95 degrees C, whereas the BA viscosities changed little at this temperature. There were no statistically significant differences among the C/S for amylose or DeltaH. However, significant C/S differences in swelling power, solubility, and pasting properties were observed. Although differences in some rheological and physical properties were observed for C/S starches, shear stress was statistically correlated only with DSC onset temperature (r = 0.78), indicating that factors other than the properties measured on isolated starches are mainly responsible for the texture of cooked SP C/S.

RVA Pasting Properties of Australian Wheat Starches

Viscosity properties of wheat starch and flour measured by the Rapid Visco Analyser (RVA) were characterised by RVA running conditions and varietal difference. RVAvariables including starting temperature of measurement, heating rate and final cooling temperature were found to be the most important factors determining RVA viscosity properties. Starting temperature mostly affected peak time, peak viscosity, breakdown and setback viscosity for starch, and peak time and breakdown for flour. Heating rate influenced peak time, peak viscosity, holding strength and final viscosity for starch, and peak time, peak viscosity, breakdown and holding strength for flour. Setback viscosity for starch and flour was determined by final cooling temperature. Discrimination of wheat varieties was greatest with the following RVArunning profile: starting temperature of 50°C, heating rate of 20°C/min and final cooling temperature for both starch and flour of 43°C. This profile also showed clear classification of wheat varieties tested and accordingly good prediction for softness of cooked white salted noodles.

Rheological Method for Evaluating Endoproteolytic Enzyme Activity

ABSTRACTA rheological method for evaluating endoproteolytic enzyme activity was developed. The decrease in viscosity as a function of time of dispersion of commercially available modified wheat gluten protein in water (15%, w/w) was measured with a rapid visco analyzer (RVA). Measurement of the RVA viscosity signal at a chosen temperature was continuous and reproducible. As described, the method also can be used to determine the temperature optima of endoproteolytic enzymes at pH values exceeding 5.5 and for partial pH‐activity profiles at different temperatures. The method is simple, reproducible, and sensitive and has obvious advantages over more labor‐intensive methods in which changes in the rheological properties (elongational viscosity, stretch ratio) of a gluten‐starch dough are evaluated as a function of time.

Optimization of Rapid‐Visco Analyser Test Conditions for Predicting Asian Noodle Quality

ABSTRACTA variety of Rapid‐Visco Analyser (RVA) operating conditions have been tested with starch, flour, and wholemeal for predicting the quality of wheats for the manufacture of Japanese white‐salted noodles. Using starch as the substrate, an initial temperature of 60°C has been found to be optimum, and the best heating time from this initial temperature to the peak temperature of 95°C was ≈6 min. Significant correlations were found between peak viscosity of starch pastes and noodle quality under these operating conditions. For flour and wholemeal samples, the correlations were not as high as for isolated starch. The correlations with wholemeal or flour and noodle quality could be improved by the addition of α‐amylase inhibitors. Measuring RVA viscosity of flour or wholemeal in the presence of silver nitrate gave viscosities which showed highly significant correlations with noodle quality. These correlations were similar to those obtained with isolated starch. It appears that the improvement is due to inhibition of the α‐amylase present in grain and flour. Correlations were also observed between flour paste viscosity and alkaline noodle quality. These could be increased either by inhibiting α‐amylase with silver nitrate or by pH adjustment with sodium carbonate but the change was not significant. The improvement of the correlations by α‐amylase inhibitors in this sample set was not as great as observed with Japanese white noodles.